BearingGate: An engineering failure analysis

TL;DR:
Some of our bearings in the Titan Extruder and Titan Aero have been failing due to a series of unfortunate events and we're really sorry about that. We have a solution to fix the problem on the way, and we'll be in a position to issue replacement parts in the next few weeks. Titan products shipping from now on will not be affected because we have a short term fix in place. If you have experienced a problem then please email us and we will get replacements parts out to you. Read on to find out the finer details on what happened.

The problem

Titan Extruders (including Titan Aero) had been out in the wild for some time before we started noticing a very odd complaint coming in from some customers. The plastic lids, which we had manufactured from tough, near-bulletproof polycarbonate plastic, were starting to crack. This seemed impossible, so as well as replacing the cracked lids we also asked customers to send them to us, for some serious investigation.

Our first suspicion was that our supplier had substituted the resin for something cheaper or not purged out the extruder properly - perhaps resulting in hydrolysis from moisture or some other material defect. We went through every batch from every moulding run, literally taking a hammer to them. No dice. Polycarbonate is as crack-resistant a material as ever (phew!).

It became apparent that polycarbonate had its own kryptonite, and that we had found it.

When the culprit was found, it wasn’t what anyone expected. It turned out that the lubricant used on some of our bearings had a chemical composition perfect for chemically-degrading polycarbonate. To observe how thoroughly chemical breakdown occurred, we even left lids to soak in hot baths of lubricant, where they more or less disintegrated.

We solved the problem of how to break bullet-proof casings. Great.

This was, to put it mildly, a problem. It only took a little bit of lubricant leaching from the bearing onto the lid for it to have a powerful crack inducing effect.

Cracking in action.

Luckily, as Sanjay explained on Reddit, only some of the bearings had been treated with this particular lubricant. We immediately changed the bearing lubricant used in Titan products, the lids stopped cracking, and everything looked to be in order.

However, it wasn’t long after that we received news that these bearings, with the new lubricant, were sometimes failing, effectively causing Titan products to cease functioning until the bearings were replaced. While we had been assured by suppliers that the new lubricant would have the same performance as the previous one (without all the lid-disintegration), this turned out not to be the case as bearings were seizing up and even rusting - a clear sign of inadequate lubrication.

The short-term solution

Finally, after several rounds of product testing, we believe we’ve reached a solution for the short-term future. We worked with IGUS to replace the problematic bearings with IGUS solid polymer bushings. The polymer they are made from has been formulated to have really low friction, eliminating the need for lubricant, so there will be no mess and no danger of cracking. In addition to not requiring lubricant and having low friction, IGUS polymers also have incredibly good wear properities, so we are confident that they will last for ages, requiring no maintenance. Lastly they’re much less prone to permanent damage from axial overtightening loads.

IGUS bushings in action

There are two downsides to this solution. The first is that these bearings need to be machined from bar stock as they were not a standard part, and the material is surprisingly difficult to machine, limiting production capacity and adding delays to stock. Additionally there is a slight increase in friction compared to a true bearing. For this reason we do not recommend the 'Slimline' motor with Titan products that use IGUS bushings, but instead a 'Compact but Powerful' motor. This will mean a slight increase in weight on the print-head, which is compensated for with the larger, higher torque motor being more reliable and easy to use on many printers.

Nonetheless, these two downsides mean that bushings aren't a perfect long-term solution for our needs.

The long term solution

The original bearings used on Titan products performed perfectly well - we have machines in our print farm that have been running almost non-stop for over a year, all using the original bearings with original lubricant. They also have less static friction than the IGUS bushings and so can run more smoothly and be used with 'Slimline' motors to save weight on the print head.

In order to switch back to bearings with the original, effective, lubricant we are changing the resin which the Titan lid is made from. We've decided to move away from polycarbonate to Tritan by Eastman. Tritan has exceptionally good chemical resistance to lubricants and has very comparable mechanical and thermal performance to polycarbonate. Making the switch will eliminate the risk of degradation and give us the freedom to use the optimum lubricant in our bearings to restore the original performance of Titan products.

Unfortunately we can't put this solution to work right away. We want to make sure that nothing like this happens again, so we're running several rounds of high-stress, long-term tests before going ahead with these changes in production.

These Titan Aeros will be having a rough time of it

How we’re going to make this right with our customers

Firstly, we would like to sincerely apologise to all those who have been inconvenienced by this series of unfortunate events, and thank you all for your patience and support. The unforeseen issue with the degradation of the polycarbonate, followed by the subsequently induced issue with poor lubrication of the bearings caught us off guard in both cases. The decision to change lubricant, which appeared to be a good, well thought out solution to the cracking problem backfired. Despite the assurances of our suppliers that the new lubricant would perform just as well as the old, the bearings began to fail.

We’re working as quickly as possible to get the long term solution of Tritan-Titan lids and optimally lubricated bearings in stock and ready to ship, but this will take some time to get both the bearings and lids in stock in enough quantity to replace faulty parts. In the short term we will be shipping out Titans with the new IGUS bearings and larger motors to customers buying from today onwards. Unfortunately we do not have the production capacity to send these new parts out to every customer who has previously experienced this issue.

However as soon as we have the new Tritan lids and optimally lubricated bearings we will begin to issue replacements to all those who are experiencing issues. This will be the easiest drop-in fix for our customers, requiring no change in motors. We stand by our product and support our customers - we are committed to making this right with our customers and are happy to issue replacements to all those who have been affected.

Additional FAQs

Will you be issuing a recall?No. This failure is not dangerous, nor is it a certainty for all Titan products. We have Titans and Aeros in-house that have been printing for thousands of hours with no problems. The fault is with a single, small part which we will be replacing free of charge for any customers who require it.

Will this affect the Lulzbot Aerostruder?No. Lulzbot have used their own bearings in developing the Aerostruder, so it should have no problems.

When will Titans without this fault start shipping?23/01/2018. If your Titan product ships on or after this date, it will not be affected by the bearing fault as it will either ship with bushings or with the improved lids and bearings. It will be clear in the Website product description whether the product you're ordering will ship with IGUS bushings or improved bearings.

Does this affect the Titan Aqua?No. Titan Aqua has a completely different axial load profile from the Titan Extruder and Titan Aero, and should not suffer any bearings failures.

How long will it be until Titans with the new bearings start shipping?We're still running stress tests, and as such our expected lead time until these better bearings go out is approximately 5-8 weeks. It will be made clear in the online product description whether the product that you buy will be shipping with IGUS bushings or improved bearings.

How do I know if my bearing is faulty?If it jams for no discernible reason, if it's broken or cracked, or if there's an accumulation of rust around the bearing, then it's faulty. This issue only affects Titan products shipped between February 2017 and January 2018. If your product was ordered outside of that window then you will not be affected.

That rust could be caused by fretting corrosion. The load rotates relative to that inner race so it should be the fixed one while the outer race could be relatively more loose-fitting.

A better design may be to have a press fit of the bearing to the shaft (easiest) or other means such as axial clamping with a threaded fastener with the goal of making sure there is no movement.

I don't know if a press-fit of the bearing to the shaft could still allow the design to be assembled but perhaps the outer race could be a slip fit into the plastic at final assembly. The loading on the outer race is fixed in one direction so the fit there is not so critical other than for accurate location.

Plain bearings such as Igus have their uses but I don't think it is good to use them when you desire precise motion control.

cheers and good luck!
Mark

PS
Sorry for the possible duplicate message, I put this through once before but I didn't receive a response so I was not sure the post was successful. Also, I have seen this problem and the solution a few times in my industry and we have also tried plain bearings such as Igus but finally our solutions are much more likely to involve properly secured deep groove ball bearings.

I had ordered the Titan Universal extruder on March 14, 2017 from Amazon (Order# REMOVED) and it was shipped on the 16th of the same month. I had noticed some small cracks starting to form in the support ring around the top bearing of the polycarbonate plate.

Can you let me know when I could pursue getting a replacement to avoid a failure?

Hi Lindsey,
I'm afraid we don't currently sell Titans on Amazon, which means that this sale would have been through a reseller and Amazon and we have no record of the sale in our own database. However, as long as you bought a genuine Titan, you can fill in the form linked in the blog post and you will receive a replacement plate when they are released.
All the best,
E3D

I bought a titan, probably after feb 2017 though i can't remember. I did have a bearing explode whilst my machine was doing a demo for some rather important visitors (not the best time but it's no big deal) . i bought some new bearings from you guys mid november. Do I need to worry about my titan breaking?

Hi Harry,
This failure is not inevitable with every bearing, and it may well work with no problems. I would recommend that you keep an eye on it and if it fails then just fill in the form linked in the post and we will replace it free of charge.
All the best,
E3D

Hello, we have just received a pair of Titan Aero extrudes(About a month ago, one normal, one mirrored), I'm assuming the black plastic of the body is also polycarbonate and thus suffers from the same problem, not just the clear lids of the Titans?
I'm also guessing that by this stage we would have the non-degrading but not-performing lubricant on the bearings?
Would adding a drop of a high quality machine oil to the bearings help solve this problem or would this only cause further problems?
I hate the idea of just sitting and waiting for something to break.
Thank you.

Hi Electra,
The black plastic body parts are made of Delrin plastic and so aren't susceptible to cracking like the Titan lids. A drop of machine lubricant would not do any harm and may prolong the life of the bearings if, indeed, yours are faulty.
All the best,
E3D

I've got a completely unused Titan plus Aero kit ready-to go, but I noticed that the polycarbonate is already stained around the the bearing.
But about that bearing: There seems to be very little lubricant in there to begin with, the bearings run very well and rattle quite a bit. Also
this type of bearing requires a preload, and polycarbonate would be a poor choice of material to put load on such a small surface.
The rust between the bearing and the pulley is likely caused by the vapors from printing PLA, which emits water steam and ethanoic acid in
small quantities. Also PLA dust is highly hygroscopic. That would be an optimal breeding ground for electrolytic decomposition of the weaker metal,
even more if the bearing itself brings an acid-rich lubricant with it. BTW: Ethanoic acid will also break down certain polycarbonates.
So, I should I not use this one with the bearings the way they are ?
Also - you recommend not to use the slim stepper with the updated bearings - and go on to say that the added force in the extrusion from a full size
NEMA17 stepper will make up for the added weight, size and vibration this brings to the printer
(apart from the fact that it might no longer fit at all) ... WHAT ?
What lubricants are safe to use with a bearing in the polycarbonate ?

Dear Dirk,
The new replacement bearings which we are currently testing will be suitable for use with a slimline motor. Only customers currently buying new Titan Extruders and Aeros will receive IGUS bushings with their parts. We'd be more than happy to discuss your further questions, and ask that you call or email support@e3d-online.com. Our team will be very happy to assist you.
All the best,
E3D

Bought a Titan Aero along with the slimline motor back in June of last year. The bearing definitely is having issues (now the rust makes sense).

Saw you guys are replacing them with the IGUS, and that they are not recommended with my motor. Would there be a way for me to get a replacement of the original bearing instead of the IGUS? I would rather not have to replace this relatively new motor.

Hi Bryan,
We recognise that this is a potential issue, so if you fill in the form at the bottom of the post we promise to replace the bearings with an improved non-IGUS bearing. We're currently testing these new bearings but they should be shipping out in a few weeks.
Lots of love from E3D

Don't know about your new plastic but many (especially the high performance) have a very similar stress cracking problem with Lock-Tite. Mite be worth checking and posting a warning incase somebody decides they want to use it.

I had the problem with my Titan Aero. The bearing on one side just disintegrated while the other just seized up. The outer race was stuck in the heatsink. I have ordered some ceramic bearings to test. I will let you know my outcome. I wonder if pressure from the spring may be to much.

I've purchased 2 Titan Extruders and a Titan Aero Upgrade kit on Amazon.com through MatterHackers and 3DMakerWorld respectively here in the US. The first Titan Extruder was ordered on Amazon March 22nd, 2017 and it's lid cracked. The 2nd Titan Extruder was ordered January 29th, 2018, and has yet to be put into service. The Aero Upgrade was ordered on Feb 8th, 2018. Would you agree that these all need bearings based on the fact that they came from US resellers from within the aforementioned timelines?

The bearing completely collapsed in mine (added a request to replace) but due to the collapse it also cause the whole drive gear to screw and has cause damage to the hobb gear as it has sat grinding against the metal filament when it got trapped by the misalignment. Will this be replaced along with the bearings and lid?